1. Weathering, Erosion, & Deposition
The surface features of the Earth change as a result of observable physical and chemical processes

2. Weathering and Erosion
This is a monument called Cleopatra’s Needle. It was carved in Egypt around 1450B.C. The sides are carved with hieroglyphs, the writing of ancient Egypt. It stood in the dry, hot Egyptian desert for over 3000 years. During that time, the hieroglyphs remained distinct.

3. Weathering
In 1800, the monument was moved to New York City. Almost immediately, the hieroglyphs began to fade. In only a few years in the wet and variable climate of New York, the Egyptian writing became indistinct!

4. Erosion
Cleopatra’s Needle was carved from granite, a hard tough, crystalline rock.
Although it is tough, granite is changed by the atmosphere.
Some of the minerals that make up granite change to clay.
Chips and flakes of minerals break away from the granite surface.

5. The Cycle of Changing Earth’s Surface
Weathering, erosion, and deposition act together in a cycle that wears down and builds up Earth’s surface
Weathering-wears down the Earth’s surface
Erosion-moves the Earth’s surface (acts as a bridge between the weathering and deposition)
Deposition-builds up the earth’s surface

6. Weathering
Erosion
Deposition

7. Weathering
The breaking down and/or wearing away of earth materials (rocks) into smaller pieces
Must occur before erosion can happen
No movement is involved

8. Physical aka Mechanical Weathering
Breaks rocks down into smaller pieces (nothing changes but the size)
Sediments: naturally-occurring material that is broken down by processes of weathering; small/tiny pieces of rock
Sediments vary in sizes and are named depending on their size

9. Weathering Physical Common weathering processes: Frost action
Thermal Expansion and Contraction
(wetting and drying)
Biological Activity
Exfoliation
Abrasion

11. Types of Mechanical Weathering
Thermal Expansion & Contraction (Wetting & Drying)
Especially effective at breaking up rocks that contain clay.
Clays swell up when wet and shrink when dry.
Causes rocks that contain clay, such as shale, to fall apart.

13. Types of Mechanical Weathering
Frost action or Ice Wedging:
Water takes up about 10% more space when it freezes.
Expansion puts great pressure on the walls of a container.
Water in the cracks of rocks wedges the rock apart when it freezes.
Often occurs in places where temperatures vary from below and above the freezing point of water.

15. These mountains in Salt Lake City were weathered by abrasion.
Abrasion is the grinding action of other rock particles due to gravity or the motion of water, ice or air.
Most often seen in running water, the beach, or the desert

17. Types of Mechanical Weathering
Action of plants and animals (biological activity)
Larger trees and shrubs may grow in the cracks of boulders.
Ants, earthworms, rabbits, woodchucks, and other animals dig holes in the soil.
These holes allow air and water to reach the bedrock and weather it.

18. Types of Mechanical Weathering Granite exfoliation

19. Exfoliation
Occurs when thin layers of rocks break off in sheets

20. Chemical Weathering
Occurs when chemical reactions dissolve or change the minerals in rocks (rusting, acid breakdown, etc)
Occurs most often in warm and humid climates
This cave was formed by slightly acidic water dissolving the limestone

21. Chemical Weathering Breaks down rock through chemical changes.
The agents of chemical weathering
Water: dissolves rock over time
Oxygen: combines with iron to form rust (oxidation)
Carbon Dioxide: dissolves in water to form carbonic acid
Living Organisms: plant roots secrete acids
Acid Rain: from the burning of fossil fuels

22. Water

23. Living Organisms
Lichens that grow on rocks produce weak acids that chemically weather rock.

24. Oxygen
Iron combines with oxygen in the presence of water in a processes called oxidation.
The product of oxidation is rust.

25. Carbon Dioxide Dissolves easily in water.
Forms a weak acid called carbonic acid
The same compound that is in carbonated drinks.
Carbonic acid easily weathers limestone and marble.

26. Acid Rain
Compounds from burning coal, oil and gas react chemically with water, forming acids.
Carbon dioxide and sulfur compounds released by industries unite with water in the atmosphere to form acid rain.
Increasing amounts of acid rain in the environment increase the rate of chemical weathering.
Acid rain causes very rapid chemical weathering.

28. Physical and Chemical Weathering
Rate of weathering depends on:
Climate—warm and humid is faster
Size of the rock particle
Mineral composition—determines how fast a rock weathers
Time—most important factor
Given enough time all rocks with weather
Rock Type—rock that is permeable (has holes that let water in), weathers faster than rock that is impermeable.
Weathering creates either sediment or soil
Classified by size—sand, silt, or clay

29. Check for Knowledge
How does the size of the rock particle affect weathering?
How does the mineral composition of the rock particle affect weathering?
Why is time the most important factor?

30. Lets compare
Please draw a Venn diagram and compare chemical and physical weathering.
How are they similar/different?

31. Erosion
The movement of weathered earth materials by moving water, wind, gravity or ice
Ex: waves causing beach erosion (shoreline of Texas is disappearing) running water
Ex: sand storm wind
Ex: rain causing a mudslide running water and gravity
Ex: landslide gravity
Ex: rain carrying soil and gravel down a driveway running water and gravity

32. What are the 4 main ways water erodes?
Runoff
Stream Erosion
Wave Action
Glaciers

33. Erosion
The Bernard Glacier in Alaska's Saint Elias Mountains looks like a huge alpine highway. Glaciers are slow but highly effective shapers of the land, essentially carrying away anything in their path—from soil and rocks to hills and even the sides of mountains

34. Why are glaciers called dirty snowballs? What is glacial till?
Glaciers are called dirty snowballs because as they move across the land they carve up the earth’s surface collecting rocks and sediments with the snow.
Glacial till is the jagged uneven particles the glacier deposits as it retreats (melts)

35. Mass Wasting and Creep Mass wasting—downhill movement by gravity
Potential increases with slope
Causes rock slides, slump, mud slides, or avalanches

36. Landslides Landslides- A geological phenomenon
Includes a wide range of ground movement, such as rock falls, deep failure of slopes and shallow debris flows, which can occur in offshore, coastal and onshore environments.

37. Slump
A steep hillside shows a spoon-shaped depression in which material has begun to slide downhill.
Occurs along a distinct fracture zone, often within materials like clay that may move rapidly downhill.
In some cases the slump is caused by water beneath the slope weakening it.

38. Soil Creep Can be almost undetectable.
Normally found on weathered mountain slopes.
Gravity forces the material to slowly slide downhill, and eventually the signs of creep become evident.
Tree trunks curve upward as creep caused them to tilt downhill
Fence posts and hydro poles may also begin to lean downslope

39. Why care about erosion?
Human activities such as construction increase the rate of erosion 200, even 2,000 times that amount. When we remove vegetation or other objects that hold soil in place, we expose it to the action of wind/water and increase its chances of eroding
The loss of soil from a construction site results in loss of topsoil, minerals and nutrients, and it causes ugly cuts and gullies in the landscape. Surface runoff and the materials it carries with it clog our culverts, flood channels and streams. Sometimes it destroys wildlife and damages recreational areas such as lakes and reservoirs.

40. Bare Slopes vs. Vegetation Stabilized Slopes
Mudslide danger
Loss of topsoil
Clogged storm drains
Flooding problems
Expensive clean up
Eroded or buried house foundations
Soil in place
Less clean up
Minimum erosion
Protection for house foundations

41. Deposition Ex: sand dune-a deposit of wind blown sand
The process of eroded earth materials (sediments) being deposited in a new location
Ex: delta-where sediment is deposited where a river flows into an ocean or lake builds up a landform
Ex: sand dune-a deposit of wind blown sand

42. Process of Deposition
When sediments are released after being transported
Usually when velocity decreases
Factors affecting deposition:
Particle size—smaller, the slower the rate
Shape—more spherical, the faster the rate
Density—more dense, the faster the rate

43. Process of Deposition Grade bedding aka Vertical Sorting
Velocity of transporting agent reduced quickly
Sediments of mixed sizes
Size of sediment increases with depth
Horizontal sorting
Velocity decreases slow rate over long distance
Larger first, smaller last—mouth of river

44. Erosion and Deposition
Meanders are S shaped curves formed by weathering of one bank of a river and deposition of the weathered sediment on the opposite bank of the river.
This creates a loop-like bend in a river.

46. Erosion Control Methods:
Riparian Buffers
Leaving undisturbed plant life on either side of a body of water to prevent erosion

48. Erosion Control
silt fencing
terracing

49. Notes quiz Deposition is the movement of sediment or rock
the settling out of sediment or rock
the breaking down of sediment or rock
2) A meander is
a) a small river that runs into a larger river
b) a loop-like bend in a river
c) a lake that has been cut off from a river

50. 3) Name 3 methods of erosion controlb) c)
4) What are riparian buffer zones?